LED Resistor Calculator
Calculate the required current-limiting resistor for an LED. Enter supply voltage, LED forward voltage, and desired forward current.
How It Works
Calculate the required current-limiting resistor for an LED. Enter supply voltage, LED forward voltage, and desired forward current. Enter your values above and click Calculate to get instant results.
Formula
R = (Vs - Vf) / If | Power = (Vs - Vf) × If
Quick Examples
- 5V supply, 2.0V red LED, 20mA → R = 150Ω
- 12V supply, 3.4V white LED, 20mA → R = 430Ω (use 470Ω)
- 3.3V supply, 2.0V LED, 10mA → R = 130Ω (use 150Ω)
Frequently Asked Questions
What is a typical LED forward voltage?
Red/Yellow/Orange LEDs: ~1.8–2.2V. Green/Blue/White LEDs: ~3.0–3.6V. Always check the LED datasheet for accurate values.
Why do I need a resistor with an LED?
LEDs are diodes with very low resistance. Without a current-limiting resistor, they draw excessive current and burn out instantly. The resistor controls current to the safe operating level.